public static BlockExpression GetInvariants(this IList <Expression> expressions, params ParameterExpression[] variables)
{
var invariants = new List <Expression>();
var invariantVars = new List <ParameterExpression>();
var vars = new HashSet <ParameterExpression>(variables);
var movedVariables = new List <ParameterExpression>();
for (var i = 0; i < expressions.Count; i++)
{
var ei = expressions[i];
if (ei is BlockExpression be)
{
foreach (var ee in be.Expressions)
{
if (ee is BinaryExpression ae && ae.NodeType == ExpressionType.Assign)
{
var left = (ParameterExpression)ae.Left;
var eei = DependencyChecker.FindInvariant(ae.Right, vars);
if (eei == ae.Right)
{
invariants.Add(ae);
invariantVars.Add(left);
ei = ExpressionReplacer.Replace(ei, ee, Expression.Empty());
}
else
{
var ee1 = ee;
vars.Add(left);
while (eei != null)
{
var t = Expression.Parameter(eei.Type);
invariants.Add(Expression.Assign(t, eei));
invariantVars.Add(t);
var ee2 = ExpressionReplacer.Replace(ee1, eei, t);
ei = ExpressionReplacer.Replace(ei, ee1, ee2);
ee1 = ee2;
eei = DependencyChecker.FindInvariant(ee1, vars);
}
}
}
else
{
var ee1 = ee;
var eei = DependencyChecker.FindInvariant(ee1, vars);
while (eei != null)
{
var t = Expression.Parameter(eei.Type);
invariants.Add(Expression.Assign(t, eei));
invariantVars.Add(t);
var ee2 = ExpressionReplacer.Replace(ee1, eei, t);
ei = ExpressionReplacer.Replace(ei, ee1, ee2);
ee1 = ee2;
eei = DependencyChecker.FindInvariant(ee1, vars);
}
}
}
}
public static Expression EliminateCommonSubexpressions(this Expression expression, ref IEnumerable <ParameterExpression> variablePool)
{
var pool = new VariablePool(variablePool);
do
{
var q = from e in ExpressionCounter.Evaluate(expression)
where e.Value.usageCount > 1 && e.Value.cost > 0
orderby e.Value.usageCount descending, e.Value.cost descending
select e.Key;
var mostExpensive = q.FirstOrDefault();
if (mostExpensive == null)
{
break;
}
// introduce a variable for mostExpensive
var t = pool.GetVariable(mostExpensive.Type);
// TODO: fix the order of the variables. Assignments should go after all depends
expression = MergeBlocks(t, mostExpensive, ExpressionReplacer.Replace(expression, mostExpensive, t, new CodeComparer()));
} while (true);
variablePool = pool.Variables;
return(expression);
}